There is a retainer clip and socket behind that it inserts in. It just pulls out work it from all four sides.There will also be two wires for the heated mirror you'll have to unclip from the back after it's popped out.
Recently side swiped my garage door track and the wife saw it all. All that was damaged was the glass only, $80 later and 30 secs of my time, new mirror and my pride was restored. Wish I had the photo of the other side.